The invention relates to an osteochondral plug graft, kit for implanting the graft and a method of osteochondral regeneration with the graft.
Human joint surfaces are covered by articular cartilage that provides a resilient, durable surface with low friction. Cartilage is an avascular tissue that has a small number of chondrocytes encapsulated within an extensive extracellular matrix. The cartilage acts to distribute mechanical forces and to protect subchondral bone. The knee is a particular instance of a cartilage surfaced (the condyle) bone area. The knee comprises three bones—the femur, tibia, and patella that are held in place by various ligaments. Corresponding chondral areas of the femur and the tibia form a hinge joint and the patella protects the joint. Portions of the chondral areas as well as the underside of the patella are covered with an articular cartilage that allows the femur and the tibia to smoothly glide against each other without causing damage.
Damage to the articular cartilage, subchondral bone or both can result from traumatic injury or a disease state. For example, articular cartilage in the knee can tear due to traumatic injury as with athletes and degenerative processes as with older patients. The knee cartilage does not heal well due to lack of nerves, blood vessels and a lymphatic system. Hyaline cartilage in particular has a limited capacity for repair and lesions in this material without intervention can form repair tissue lacking the biomechanical properties of normal cartilage.
A number of procedures are used to treat damaged articular cartilage. Currently, the most widely used procedure involves lavage, arthroscopic debridement and repair stimulation. Repair stimulation is conducted by drilling, abrasion arthroplasty or microfracture. The goal of this procedure is to penetrate into subchondral bone to induce bleeding and fibrin clot formation. This promotes initial repair. However, the resulting formed tissue is often fibrous in nature and lacks the durability of normal cartilage.
Osteochondral grafting has been used to repair chondral damage and to replace damaged articular cartilage and subchondral bone. First in this procedure, cartilage and bone tissue of a defect site are removed by routing to create a bore of a precise cylindrical geometry. Then a cylindrical cartilage and subchondral bone plug graft is harvested in a matching geometry. The harvest is typically from another body region of less strain. The plug graft can be harvested from a recipient source (autograft) or from another suitable human or other animal donor (allograft). The harvested plug graft is then implanted into the bore of the routed defect site. Healing of the graft bone to host bone results in fixation of the plug graft to surrounding host region.
Surface characteristics of the plug graft are critical. For a successful procedure, surface of the transplanted graft must have the same contour as the excised osteochondral tissue. If the contour is not a correct match, a repaired articular surface is at risk for further damage. Typically implants are harvested and press-fit into a prepared recipient socket at a patient's defect area. Success of the grafting process is dependant on the seating of the implant within the socket. First, surface characteristics of the implant are critical. For a successful procedure, surface of the transplanted implant must have the same contour as the excised osteochondral tissue. If the contour is not a correct match, a repaired articular surface is at risk for further damage. Additionally, some implant shapes do not pack well into irregular defects. The implant may have a propensity to rotate. Rotation can result in poor integration of the implant with surrounding host tissue. An improperly place implant can result in host tissue integration failure and post implantation motion.
Since the implant is press-fit within a recipient socket, removal can cause irreparable damage that can render an implant useless. Hence, a surgeon has only one opportunity to properly press fit the implant. If the implant is placed too shallow or too deep or otherwise incorrectly, the implant cannot be removed for proper replacement by typical procedures or tools. Extraction procedures and tools can cause damage to boundary implant cells and to implant structural integrity.
There is a need for an osteochondral implant, kit and method to permit implant replacement without damage.